This invention relates to a method of steering a mining machine and particularly, although not exclusively, concerned with the steering of a double-ended ranging drum mining machine. It also has reference to the steering of a single-ended ranging drum mining machine.
Such machines are used particularly in mining minerals, such as coal, where the desired mineral is extracted from a seam by a long-wall mining method. In the long-wall mining method the machine successively traverses across a face which may be of the order of 250 m in length, cutting the mineral as it goes. In the case of a double-ended ranging drum machine, the machine carries a rotating cutting drum at each end of its ranging arms and one of the drums cuts, as a leading drum, the top of the seam while the other, the trailing drum, cuts the lower part of the seam.
It is necessary in order to maximize the economics of the mining operation to ensure that the fullest extraction of the desired mineral from the seam is taken, without there being any excursion by the cutting drums into the overlying or underlying strata. This is usually achieved by determining that a desired thickness of the mineral is left at the roof and the floor. Roof coal also helps in stabilizing roof conditions. A typical thickness is of the order of 100 mm.
One way in which this roof thickness is maintained is by measuring the amount of natural gamma radiation emitted by the adjacent strata as described in assignee's British Patent No. 1 526 028. This radiation can be picked up by a gamma detector situated on the machine and the strength of the signal received is dependent on the attenuation of the signal by the quantity of roof left after the cutting operation. If the signal is attenuated too far as the thickness increases, then a correction steering signal can be given to alter the angle of the ranging arm to alter the cut so that a lesser thickness of roof is left.
However, in order to achieve this, it is also necessary to measure physically the roof step, the difference in roof heights between the previous pass cut roof, at which a roof coal thickness measurement is available, and the leading or roof cut drum, in order that further steering of the drum can take place. Currently, this is usually done by using a roof follower which is attached to the ranging arm itself. This follower contacts the roof, cut on the previous pass, but adjacent to the drum, and physically follows its contours. As deviations occur, a transducer produces electrical signals which can be fed to a comparator for altering the angle of the ranging arm as necessary. For a double-ended ranging drum mining machine, the trailing drum must be positioned with respect to the cut roof to provide the correct extraction. Extraction control for a single-ended ranging drum mining machine is currently controlled using stored boom height. The roof cut may be made with the drum leading or trailing.
The steering may also be controlled by a factor which takes account of the inclination or tilt of the machine towards the face.
Particularly in deep seams, the roof follower, which is located in a vulnerable position close to the drum, may be a very long cantilevered arm and thus quite flexible and liable to damage, for example by mineral falling from the roof or by irregularities in the roof itself.